1. Field of the Invention
The present invention relates to an organic electroluminescence (hereinafter referred to as EL) panel and a method of manufacturing the same, and more particularly to an organic EL panel provided with partitions for separating pixels and to a method of manufacturing the partitions.
2. Related Arts
An organic EL panel having such partitions is disclosed in Japanese Unexamined Patent Publications No. Hei 9-102393 and Hei 8-315981. According to the organic EL panel manufacturing method disclosed in these publications, as is shown in FIG. 1A, anodes, transparent electrodes 2 composed of indium tin oxide (hereinafter referred to as ITO), are formed as stripes on a transparent substrate 1, and to separate the pixels, photolithography is used to form electrical insulating partitions 31 that cross and that are perpendicular relative to the transparent electrodes 2. The lower portions of these partitions 31 are tapered invertedly, and their upper portions constitute overhanging portions 310. Then, as is shown in FIG. 1B, using a film deposition mask 37, an organic emission material that emits only one color is deposited on the transparent substrate 1, on which the partitions 31 are formed, at angles indicated by arrows P and Q, so that the organic emission material extends outward to either side and under the overhanging portions 310. This deposition process is repeated for each color to obtain an organic emission layers 32. Thereafter, as is shown in FIG. 1C, to form cathode electrodes 33 on the partitions 31 and the emission layers 32, the film deposition mask 37 is removed and a cathode electrode material is deposited in the direction, as is indicated by arrows S, that is substantially perpendicular to the transparent substrate 1. Since each partition 31 has overhanging portions 310, the cathode electrode 33 on each side of a partition 31 is electrically insulated.
As is shown in FIGS. 1A to 1C, the partitions 31, which are obtained by using a resist to provide an invertedly tapered shape, are employed to separate pixels and cathodes. When a resist is employed, however, the resist""s residual developing liquid, an etching liquid and a small quantity of water act together to cause deterioration of the interfaces of the organic emission layer 32 and the cathode electrodes 33. As a result, a non-emission point called a dark spot is generated. The generation of a dark spot makes it difficult to extend the service life of a panel. The overhanging portions 310 of the invertedly tapered partitions 31 are formed by using a difference in the developing speeds that is the result of differences in the light exposure volumes in the direction of thickness. Thus, the sizes of overhanging portions 310 are unstable and insufficient separations tend to occur. When an insufficient separation occurs, not only are a cathode electrode 33 and an anode, transparent electrode 2 short-circuited and a non-emission element generated, but also the panel may be damaged by heat due to the short-circuit. In addition, for such a display panel, the partitions 31 must have, at the least, a predetermined width in order to prevent insufficient separation, so that the area required for the partitions 31, which serve as non-light emission portions, is increased. As a result, the aperture ratio can not be increased, and it is difficult to attain a smaller pixel size.
It is, therefore, one objective of the present invention to provide an organic EL panel for which a smaller pixel size can be attained and for which productivity can be enhanced, and a manufacturing method thereof.
It is another objective of the present invention to provide an organic EL panel that is obtained as an apparatus having a smaller feature size and high image quality, and a manufacturing method thereof.
To achieve these objectives, the present inventors have devoted their time and effort to developing methods by which to acquire a smaller feature size for an organic EL panel and by which to improve productivity. As a result, the inventors were able to devise an effective method to use for forming partitions for separating pixels. According to this method, after a charge generation layer and a charge transfer layer have been formed on a transparent electrode, an electric charge is applied to the charge transfer layer and the charge generation layer is selectively exposed to form on it an electrostatic latent image having a predetermined pattern. Then, a developing agent is used to develop the electrostatic latent image, and the developed image is fixed, forming partitions. After the inventors developed this idea, they applied it in the fabrication of an organic EL panel and in the development of a manufacturing method in accordance with the present invention.
Specifically, according to one aspect of the present invention, a method for manufacturing an organic EL panel comprises the steps of:
forming on a transparent substrate a first electrode that is made of a transparent material;
forming a charge generation layer and a charge transfer layer, in the named order, on the first electrode;
charging the charge transfer layer, and then selectively exposing the charge generation layer so as to form, on the charge transfer layer, an electrostatic latent image having a predetermined pattern;
forming, on the charge transfer layer, a developing agent pattern that corresponds to the electrostatic latent image;
forming the developing agent pattern as partitions for separating pixels; and
forming an emission layer and a second electrode between the partitions.
Since with this method the generation and growth of dark spots can be prevented, productivity can be improved.
The method of the present invention, for manufacturing an organic EL panel, includes a manufacturing method whereby, after a mask having a predetermined pattern that leaves at least a part of the charge transfer layer exposed is mounted on the partitions, the emission layer and the second electrode are formed by vacuum deposition, or whereby the emission layer and the second electrode are formed by oblique deposition.
The developing agent used in the method of the present invention for manufacturing an organic EL panel is a mixture of a charge control agent and at least one material selected from among polyester, acryl and styrene-acrylic copolymer. Furthermore,the developing agent may contain a black material to form black partitions. The developing agent may further contains a magnetic powder.
According to another aspect of the present invention, a method for manufacturing an organic EL panel comprises the steps of:
forming on a transparent substrate a first electrode that is composed of a transparent material;
forming a charge generation layer and a charge transfer layer, in the named order, on the first electrode;
charging the charge transfer layer;
selectively exposing a predetermined area of the charge generation layer so as to form, on the charge transfer layer, an electrostatic latent image having a predetermined pattern;
developing the electrostatic latent image to form a developing agent pattern;
fixing the developing agent pattern to the charge transfer layer to form partitions; and
forming an emission layer and a second electrode, in the named order, between the partitions.
In addition, according to an additional aspect of the present invention, an organic EL panel comprises:
a transparent substrate;
a first electrode, composed of a transparent material, that is formed on the transparent substrate;
a charge generation layer covering the first electrode;
a charge transfer layer formed thereon;
partitions formed on the charge transfer layer by using a developing agent pattern having a predetermined shape; and
an emission layer and a second electrode formed between the partitions.
The organic EL panel of the present invention includes following features that the width of each of the partitions is 10 to 40 xcexcm and the partitions are black.